1. Field of the Invention
The present invention relates to a method for setting up a perch channel to be allocated to each base station in a mobile communication by a cellular system in which a plurality of service areas are provided by a plurality of base stations.
2. Description of the Background Art
In the cellular system, a perch channel is allocated to each base station, and each base station carries out a signal transmission through the allocated perch channel as well as a signaling of perch channel list for surrounding base stations. A mobile station measures reception levels of perch channels, and makes a selection of the closest base station and a selection of a moving destination base station according to the measured reception levels. After the perch channel list for surrounding base stations is received at the mobile station, the perch channels for which the reception level measurement must be carried out by the mobile station can be narrowed down, so that it becomes possible to carry out the reception level measurement at high precision in short time. A standard for utilization of perch channels in cellular systems is described in "Personal Digital Cellular Telecommunication System Standard RCR STD-27."
However, when the mobile station does not have the perch channel list for surrounding base stations, there is a need to carry out the reception level measurement for all the perch channels. In order to shorten the time required for this reception level measurement, the cellular system adopts a scheme for arranging perch channels by reusing the same perch channel at different service areas so as to reduce a number of perch channels.
In arranging the perch channels, there is a need to arrange the identical perch channels with a sufficient distance provided therebetween so as to prevent an interference between the identical perch channels. In the conventional cellular system, such a setting of the perch channels has been made by a system designer. In an initial arrangement at a time of system design, the propagation characteristics are estimated according to the geographical conditions, and the identical perch channels are arranged with a sufficient reuse distance therebetween for preventing a mutual interference. In addition, a perch channel list for surrounding base stations to be signaled by each base station is also set up. Also, at a time of providing a new base station, an available perch channel is selected and a perch channel list for surrounding base stations is set up, according to the utilization state of the perch channels at the surrounding base stations.
Now, it is expected that a subscriber capacity required for the cellular system will continue to increase, and there will be a constant need to provide a new base station according to the increasing demand. In the conventional perch channel set up method, the perch channels are to be set up by a system designer every time a new base station is provided, so that there has been a drawback regarding a considerable amount of work load required for the system designer.
In addition, the propagation characteristics are not actually measured but only estimated, so that there has been a possibility for the perch channels to interfere with each other.